The present invention relates to composites of plastic films containing a barrier layer against permeability, and also relates to the use of said composites for the manufacture of packaging forms.
To be understood as packaging forms here are in particular pouches such as sealed seam pouches, tube shaped pouches, salt-standing pounces, sachets, sacks, bags, and wraps for example for foodstuffs and foodstuff preparations.
For example, products of the foodstuff and semi-luxury consumables industry that perish easily or otherwise exibit impaired quality during storage, must be protected by means of suitable packaging materials from external influences such as foreign aromas, odors, moisture, penetration of oxygen, microbial effects, and from loss of substances to the outside. This protection can be achieved by incorporating barrier layers or barrier layers against permeability in the packaging material, for example, aluminum foil, EVOH or PVDC.
The disadvantage of aluminum foil is the large mount of energy required for its primary manufacture and its influence on the purity requirement for recycling packaging materials. EVOH is sensitive to moisture and gives rise to difficulties during manufacture; PVDC. as with all chlorine-containing plastics, is undesirable from the environmental standpoint.
For flexible packaging purposes, e.g. for pouches, considerable use is made today of composites in the form of laminates comprising different kinds of tightly-bonded films, foils and/or other layers, such as e.g. adhesives or barrier layers. The aim is to usefully combine the properties of the individual components. One important aspect of using such packaging is the resistance to conservation processes that as a rule take the form of thermal treatments such as pasteurization, sterilization, or aeseptic treatments.
Known for example from EP-A 0 240 571 are pouches of polyester (25 .mu.m)/silicon oxide (600 .ANG.)/cast polypropylene (70 .mu.m) that are intended for containing cooked and processed foodstuffs. Long-term storage tests show that pouches made from such composites, do not provide convincing results with respect to the shelf-life of their contents.